Turbine wheel construction



TURBINE WHEEL CONSTRUCTION Arthur J. Slemmons, Birmingham, Mieh., assignor' to Chrysler Corporation, Highland Park, Mich., a corporation of, Delaware Application MarclilS, 1954, Serial No. 416,052.

Claims. (Cl. 253-49) invention. relates. to. elastic fluid turbine. enginessand; more. particularly to, a new and novel. turbine wheel construction for use therein.

Atypical turbine wheel installation includes, at least one circular turbine wheel which comprises. a. circular hub or disc portion and a rim portionsecured. to the periphery thereof. The rim. portion includes, a plurality ofi turbine blades disposedv atv circumferentially spaced, intervals and the circular, hub. portionincludes, a mounting meansfor; adapting thewheelfor rotation about its, central axis. High velocity combustion gasesareadapted topass through, the. blades. and. impart. a. driving torque tothe wheeL, 'Ihestress distribution. in..such.,a turbine wheeLis. such;that.. total maximum. stress; at. the. center, portion, of the. wheel is. considerably, greater; than. the. stressat theradially outward. portion nearthe .rim.

The: blades andtheri'm portion ofthe turbine wheel. normally beeomeheated to.elevatedtemperatures by the motive. gases during operation of ,the. engine.- Therim portion. therefore tends to. expand. because of. the temperaturerise, but is. restrained from doing soby thev hub. portion. to: which it isnsecured. Because of this restraint, thermal stressesare transmittedv totheinner portion of, the. hub whichcombine with the dynamic. stresses, that are producedtherein duetorhigh, speed rotation of the. turbine. wheel.

It iszanobjectof, the presentinvention to. provide. a. turbine. wheel assembly whicliincludes. a meansfor. reducing'the thermal stresses and for. correspondingly re,- ducing the maximum.- total; stress 1 in, the center portion. oftthe hub:

Armore specifieobject. of, the, present invention, is to. provide. a. turbine assembly comprising a;hl1b,diSC..ha-V7 ing; a thickness which tapers from; a maximum at the. radially inward portion to a minimum. near, the. outer edge and comprising further a peripheral axially ex tending, flange on shroudto which a plurality of. turbine, blades. may be integrally secured.

Itis another objectof the present. invention to provide a". turbine assembly as; set forth in the preceding object. wherein a plurality-of'ribsare formedunder the peripheral flanges, one-of the ribs being in the proximate vicinity of each blade.

It is another object of the present invention to provide a turbine wheel as; set forth above wherein. the same comprises a single integral castingof a suitable heatresistantmetal' alloy;

It-is a further object of the present invention, accord ing, to, a. modified form, thereof, to provide aturbine wheel. comprising a hub, and an integrally cast rim structure wherein therim structure includes. a radially extending annular web upon which the-turbine. blades are integrally secured, wherein integral rib members are. formed. below the blades, and. wherein the. hub andrim structure: arenickel brazed -to form: one. integral assembly. For: the purpose. of particularly; describing theainstant invention as required by the. patent; statutes,v reference; will. be made to the. accompanying drawings. wherein:

Figure 1 is a side view of an integrally, cast turbine. wheel of the instant invention;

Figure 2 is a radialsectional view of: aportionofthe turbine wheel of Figure l;

Figure 3 is a perspective view of asection. of; thetur bine wheel shown in. Figurev 1;.

Figure 4-is a, partial sectionallyiew of".amodifiediform.v

ofthe invention;

Figure 5 is a partial sectional, view-of another modified form. of the invention showing a vtwo-piece construe? tion.

Referrin-ggfirst .to. Figures 2 1, .2, .-and..3-, the. turbine. wheel therein illustrated) comprises a. singleunitary cast; struce ture generally designated. bynumeral. 10* which comprises a circular disc portion or disc hub 12 with asuitable central aperture 14 for, facilitating the: mounting of. the. Wheel upon a suitable turbineshaft;

The thickness. of the hub, disc 12. varies in thickness from a maximum at thecenter portion thereofto a.minimum, at the radially outward portion near the. outer: periphery.- These thicknesses are designated in Figure. 3 as z f and t f respectively; In order tobe cf;- fective inreducing the aforesaid, thermal stresses, the. axialthickness of; the wheelmust-bedecisively reduced adjacent its. outer periphery which is exposed. to the; hot motivezor driving gases, sqthati; the regionofminimum; thickness t must as least bBz'I'Hdi3l1Y1Ol-1tW3Idl-Ofi the-outer. fiflh 0f the distance from the .center of;the disc 12 to the outer periphery of-- the wheel, rim 1,6,,, as illjusa trated. V

The. axially I extending; rim or; shroud. 16 is; integrally, formed about the outer periphery; of;,the,-disc.- 12 and1,is adapted to serve as a base upon which a plurality ofi. blades. orvanes- 18 are integrally formedatspaced intervals. A plurality of. ribs 20'. are.-. provided, as, shown, under the shroud, 16 on either side ofthe disc;1 2 The: ribs 20 are cast integrally with the disc 12 and. the shroud.- 16 and are preferably spaced about. the; peripheral, edge? of the disc 12 so that one rib will be disposedradially inward of f each blade- 18.

Referringnext to the modification. of. Figure" 4,. thee turbine wheel, therein; illustrated, is; seen to also comprise; ahuh disc. 42, whichcorrespondsto disc. 1210f, Figures: 1, 2, and. 3,,ashroud46, whichcorrespondto shroud. 1601. Figures 1,2, and}, and.ribs;50, which correspond; to ribs; 24) ofFigures 1,, 2, andi.3 ;v The modification; of; Figure 4 is distinguishedfromthat.of.Figures-1,,2,,,and 3 in that. the; radially" outward. portion; of the disc 42. is formed into a radially extending web portion 43. which.

has an, axial transverse thickness; that; is; considerably less;

than the. transverse thickness ofithe'. disc at; any" point: radially inward of the web 43.

The shroud 46 blendsainto the'web 50 on either side. thereof with relatively large radii, which are: shown: at" r and r thereby avoiding the possibility of' producing; an undesirable stress concentration at these. locations;

The ribs 50 are cast integrally with the web-44 and i subjected to compressive which exist in the center portion be-low'er by virtue of the reduction in the magnitude of 'the thermal stresses being transmitted thereto by the aassssa 3 70 by nickel brazing. The nickel brazed juncture is generally designated by numeral 44.

When the turbine wheel of the present invention is subjectedto elevated operating temperatures, the radially outward portion of the assembly will tend to expand. Because relative movement between the outermost portions of the wheel and the thicker portion of the disc is restrained .by virtue of the integral construction of the wheel, the outer shroud and the adjacent web portion or peripheral disc portion will be subjected to compressive stresses in excess of the elastic limit of the constituent material and will deform plastically in the tangential direction. When the wheel assembly is cooled, the outer shroud and rib will be subjected to a residual tensile Z stress. During subsequent operation of the assembly at elevated temperatures the residual tensile stresses will become relieved and the fibres in the shroud and in the web for adjacent peripheral disc portion will again be stresses as before.

The tangential force which is produced in the peripheral portion of the assembly is a function of the cross sectional area of this peripheral portion. This cross sectional area is reduced to a minimum by virtue of the webbed construction of the present invention and therefore the tangential forces produced in the peripheral portion are also reduced to a minimum. It therefore follows that the thermal stresses transmitted to the hub disc by the heated peripheral portion of the assembly are also red'ucedto a minimum. The total combined stresses of the hub will therefore heated peripheral portion.

Since the maximum stress normally occurs at the center of a rotating turbine wheel, such a reduction in the maximum total stress at this location will materially increase the durability of the assembly andwill adapt the wheel for relatively higher operating speeds and operating temperatures.

Although certain preferred embodiments of the invention have been specifically disclosed, it is contemplated that certain varitions thereof may be made without departing from the scope of the present invention as defined by the appended claims.

I claim: 1. A high speed turbine wheel for a gas turbine engine exposed at its outer periphery during operation to high temperature driving gases, sa1d wheel comprising a circular disc having a central hub adapted to be mounted on a turbine shaft, an annular rim extending around said disc, a plurality of circumferentially spaced blades extending radially outwardly from said rim, means for minmizing the thermal and centrifugal stresses in said rim and hub during high temperature and high speed operation of said wheel comprising a decisive reduction in the axial thickness of said wheel at a plurality of locations arranged symmetrically around the periphery of said disc at its juncture with said rim, said locations of reduced axial thickness being spaced by symmetrically arranged radial ribs extending inwardly from said rim and terminating at the outer region of said disc adjacent and radially inwardly of said locations of reduced axial thickness, said ribs being integral with the juxtaposed portions of said rim and disc and being effective to transmit portions of the stresses from said rim to said disc, the region of minimum axial thickness of said wheel being radially outward of the outer fifth of the distance from the center of said disc to the outer periphery of said rim.

2. A high speed turbine wheel for a gas turbine engine exposed at its outer periphery during operation to high temperature driving gases, said wheel comprising a circular disc having a central apertured hub adapted to be mounted on a turbine shaft extending into the hub aperture, an annular rim extending around said disc, a plurality of circumferentially spaced blades integral with and extending radially outwardly from said rim, means for minimizing the thermal and centrifugal stresses in said rim and hub during high temperature and high speed operation of said wheel comprising a decisive reduction in the axial thickness of said wheel at a plurality of locations arranged symmetrically around the periphery of said disc at its juncture with said rim, said locations of reducing axial thickness being spaced by radial ribs extending inwardly from said rim and terminating at the outer region of said disc adjacent and radially inwardly of said locations of reduced axial thickness, said rim extending axially in opposite directions beyond said locations of reduced axial thickness, said ribs being arranged symmetrically around said Wheel at opposite sides thereof and being integral with the juxtaposed portions of said rim and disc to transmit portions of the stresses from said rim to said disc, and the opposite sides of said disc converging toward each other from a maximum thickness at the region of said hub to a minimum thickness at said locations of reduced .axial thickness, the region of minimum axial thickness of said wheel being radially outward of the outer fifth of the distance from the center of said disc to the outer periphery of said rim.

3. A turbine wheel according to claim 2 wherein said rim, blades, ribs, and an outer peripheral portion of said disc constitute one integral casting brazed to an inner portion of said disc around the outer perirphery of the latter portion.

4. A high speed turbine wheel for a gas turbine engine exposed at its outer periphery during operation to high temperature driving gases, said wheel comprising a circular disc having a central apertured hub adapted to be mounted on a turbine shaft extending into the hub aperture, an annular rim extending around said disc, a plurality of circumferentially spaced blades integral with and extending radially outwardly from said rim, means for minimizing the thermal and centrifugal stresses in said rim and hub during high temperature and high speed operation of said wheel comprising a decisive reduction in the axial thickness of said wheel at a plurality of locations arranged symmetrically around the periphery of said disc at its juncture with said rim, said locations of reduced axial thickness being spaced by symmetrically arranged radial ribs extending inwardly from said rim and terminating at the outer region of said disc adjacent and radially inwardly of said locations of reduced axial thickness, said rim extending axially in opposite directions beyond said locations of reduced axial thickness, said ribs being arranged symmetrically around said wheel at opposite sides thereof and being integral with the juxtaposed portions of said rim and disc to transmit portions of the stresses from said rim to said disc, and the opposite sides of said disc converging toward each other from a maximum thickness at the region of said hub to a minimum thickness at said locations of reduced axial thickness, one of said ribs being located adjacent each of said blades at each side of said disc, the region of minimum axial thickness of said wheel being radially outward of the outer fifth of the distance from the center of said disc to the outer periphery of said rim.

5. A high speed turbine wheel for a gas turbine engine comprising a central hub adapted to be mounted on a turbine shaft, a disc coaxial with said hub and extending radially outwardly therefrom, said disc having an inner portion integral with said hub and having an outer portion of heat resistant material carried by said inner portion to comprise a unitary structure therewith, said outer portion having an integral annular outer rim exposed to the high temperature driving gases of said turbine engine during operation of the latter, a plurality of blades carried by said rim and extending radially outwardly therefrom, means for minimizing the thermal and centrifugal stresses in said rim and hub during high temperature and high speed operation of said wheel comprising a decisive reduction in the axial thickness of said wheel at a plurality of locations arranged symmetrically around the periphery of said disc at its juncture with said rim, said locations of reduced axial thickness being spaced by symmetrically arranged radial ribs extending inwardly from 5 said rim and terminating adjacent said juncture to transmit stresses from said rim to the inner circumferential regions of said outer portion, said ribs being integral with said outer portion and rim, the region of minimum axial thickness of said wheel being radially outward of the outer fifth of the distance from the center of said disc to the outer periphery of said rim.

References Cited in the file of this patent UNITED STATES PATENTS Prescott Aug. 22, 1905 Keller Nov. 14, 1905 Keller Jan. 15, 1907 Melchior Mar. 31, 1925 Price Feb. 6, 1951 Grantham July 27, 1954 Bodine Oct. 1, 1957 

